Propelling charge for solid-fuel rockets



July 12, 1966 H. RENNER ETAL 3,

PROPELLING CHARGE FOR SOLID-FUEL ROCKETS Filed Jan. 25, 1963 2Sheets-Sheet 1 3n ven for: I /erm 1 Refine/- Kan-Z 02. Wei 20w 74 fin.

y 1966 H. RENNER ETAL PROPELLING CHARGE FOR SOLID-FUEL ROCKETS FiledJan. 25, 19s:

2 Sheets-Sheet 2 ATTORNEY5 United States Patent 3,260,045 PROPELLINGCHAR E FOR SOLID-FUEL ROCKETS Hermann Renner and Karl-Otto Wehlow,Dusseldorf, Germany, assignors to Firma Rheinmetall G.m.b.H.,Dusseldorf, Germany Filed Jan. 25, 1963, Ser. No. 253,883 Claimspriority, application Germany, Jan. 30, 1962, R 31,998 2 Claims. (Cl.Gil-35.6)

This invention relates to a propelling charge for solidfuel rockets. Itis a requirement in particular for the propelling charges of solid-fuelrockets that the rocket should exhibit a constant impact diagram ortarget pattern within a certain temperature range, so as to enable theprojectile to be used within the required temperature range withuniformly good hitting results, independently of any temperature controlsystem. This temperature requirement generally extends over a fairlylarge zone of the negative and positive temperature range.

When these requirements are taken into consideration, however, problemsof interior ballistics arise, since every powder has a lower burningrate at negative temperature and a higher burning rate at positivetemperature, in relation to the normal temperature, because of thephysical and chemical properties inherent in it and the nature of theburning process resulting therefrom.

This property of the powder must be taken into consideration when thefiring table is drawn up. This temperature dependence of the burningrate of the powder is particularly disadvantageous in rockets, since ifthe constriction ratio (ratio of the surface of the powder to the nozzlecross-section) is planned to be constant for the entire temperaturerange, there is obtained at low negative temperatures a greater burningtime of the rocket which, moreover, results in a poorer specific impulseowing to the lower combustion chamber pressure developed. The firingrange is thereby decreased and the dispersion of the impact diagrambecomes greater.

This eliect is of even greater importance, for example, in the case of adouble-base powder (Ngl-Nc powder) which, in certain circumstances,owing to various additions, for example of lead salts for correcting theburning rate, exhibits a zone of unsteadiness in the burning rate as afunction of the pressure, it being possible for the burning rate aboveand below this zone to be very different. For this reason, the operatingrange of the rocket should be located either above or below the zone ofunsteadiness.

If, for reasons of construction, the rocket is so designed that, byreason of the temperature requirement, the equilibrium pressure of thecombustion chamber for a certain temperature range is above and, for theremainder, in or below, the range of unsteadiness, the drawbacksdescribed make themselves noticeable to a particularly serious extent.In certain circumstances, the rocket may become totally unusable in thetemperature range in which the unsteadiness lies because of too marked adispersion.

According to the invention, the drawbacks described can be reduced inrockets having loosely inserted internally burning propelling charges inthat changes due to temperature in the physical properties of thepropellant (dimensions, solidity etc.) are used to compensate changes inthe chemical behavior (burning) which are likewise due to temperature.The invention can be carried into effect very advantageously in that thechanges in the dimensions of the propellant body are used through thecoefiicient of expansion to change the construction ratio. This can beeffected, for example, by changes in the dimensions of the propellingcharge body varying the cross section of the nozzle directly or by wayof suitable intermediate elements, whereby a change in the constrictionratio is likewise obtained.

As a further advantageous development of the inven tion, changes in thedimensions of the propelling charge body which are due to temperaturecan also be used to build up tensile and/or bending stresses in the wallof the body which result in deliberate breaking up of the latter andthereby enlarge the effective, i.e. burning, surface, whereby theconstriction ratio is likewise aflected. This can be brought about in avery simple and suitable manner by providing the propelling charge bodyat its inner and/or outer periphery with one or more longitudinalgrooves which, when the pressure increases inside the propelling chargebody, promote, as predetermined breaking point or points, the formationof cracks.

Further details of the invention are elucidated in the description ofthe example of embodiment illustrated in the drawing, in which:

FIGURE 1 is across-section of a rocket;

FIGURE 2 is a partial longitudinal section thereof;

FIGURE 3 is a cross-section of the rocket showing the propelling chargeafter formation of a crack, and

FIGURE 4 is a perspective view of a sealing strip.

Referring to the drawings, the reference 1 designates the cylindricalwall casing of the combustion chamber in which is arranged thepropelling charge 2 formed as an internal burner. Between the wall ofthe combustion chamber and the outer periphery of the propelling chargebody 2 there is an annular gap 3, the width of which is subject tochanges due to temperature, since the wall of the combustion chamber andthe propelling charge body have different coeflicients of expansion. Thewidth of the annular gap 3 is so calculated that, at normal temperatureat approximately 10 C. or 15 C. as examples, the propelling charge bodycan easily be pushed into the combustion chamber. In the uppertemperature range, the wall of the propelling charge body is thenapplied tightly against the wall of the combustion chamber, while atfalling temperatures a widening annular gap is formed. At the ends ofthe propelling charge body the annular gap is sealed by means of sealingrings 4, 4' at least one of which is so movable that changes in thelength of the propelling charge body can be taken up. The hollowpropelling charge body has internally a star-shaped crosssection inorder to obtain a large surface (burning area) and is provided, forexample, with two opposite notches (predetermined breaking points) 5, S.In the region of the notch 5 there is provided at the periphery of thepropelling charge body a further notch 6 into which there is provided anelastic sealing strip 7 with a V-shaped profile. When a longitudinalcrack is produced in the zone of the notch 5, the burning area isincreased by twice the cross-section of the crack. The sealing strip ispressed against the Wall of the combustion chamber by the pressureobtaining therein, the two sides of the seal spreading open andmaintaining their bearing action against the propelling charge body. Inthis way, the interior of the propelling charge body continues to bekept under pressure and any entry of the combustion chamber pressureinto the annular gap is prevented. Furthermore, it is made possible inthis way to obtain an area increasing in size by stages forcorresponding temperature ranges. By appropriate utilization of theelasticity properties of the propelling charge body in combination withnotches formed in varying widths, the eflect can be so controlled thatin the positive temperature range above the normal temperature mentionedno crack is formed through the body bearing against the wall of thecombustion chamber, one crack, for example, is formed as from a certainlower temperature, below the normal temperature mentioned and anothercrack at even lower temperatures through the further embrittlement andmore intensive bending open of the propelling charge body.

FIGURES 3 and 4 better illustrate particularly the elastic sealing strip7 which has a V-shaped profile. FIG. 3 thus shows in cross-section aview similar to FIG. 1 which is a cross-section of a rocket and whichillustrates the propelling charge 2 immediately after the formation of acrack in the direction from the notch 5 down into the further notch 6.The sealing strip 7 is V-shaped as clearly shown in FIG. 4 which is aperspective view of a portion of the strip and tis sealing strip hasbeen forced in FIG. 3 against the cylindrical wall casing 1 with theside portions of the strip forced against the sides of notch 6. Theinner portion of the propelling charge is held under pressure by theV-shaped sealing strip 7 and thus the sealing strip, since it is pressedagainst the wall of the chamber 1, will prevent the combustion gasesfrom entering the annular gap 3. It is to be observed that the drawingas to the original FIG. 1 shows the annular gap on quite an enlarged andexaggerated scale so that it can be readily observed, but actually thisgap is extremely small.

What we claim is:

1. A rocket propelling means for solid-fuel motors,

comprising a casing, a propellant charge of the internal burning solidtype in the casing and spaced by a gap therefrom, a longitudinallyextending notch provided on the outer periphery of the propellantcharge, said notch being of suflicient radial depth so that a crack isformed due to combustion pressures between the inner and outer surfacesof the solid propellant charge adjacent the notch, and sealing means inthe notch to seal off the outer surface of the solid propellant chargefrom the burn area, said crack providing increased burn area.

2. A rocket propelling means for solid-fuel rocket motors according toclaim 1, in which the sealing means comprises an expansible elasticstrip.

References Cited by the Examiner UNITED STATES PATENTS 2,816,418 12/1957Loedding 6039.47 2,937,493 5/1960 Adelman 6035.6 3,048,968 8/1962Hutchinson 6 )35.6 3,066,481 12/1962 George et al. 6035.6

MARK NEWMAN, Primary Examiner.

SAMUEL LEVINE, Examiner.

C. R. CROYLE, Assistant Examiner.

1. A ROCKET PROPELLING MEANS FOR SOLID-FUEL MOTORS, COMPRISING A CASING,A PROPELLANT CHARGE OF THE INTERNAL BURNING SOLID TYPE IN THE CASING ANDSPACED BY A GAP THEREFROM, A LONGITUDINALLY EXTENDING NOTCH PROVIDED ONTHE OUTER PERIPHERY OF THE PROPELLANT CHARGE, SAID NOTCH BEING OFSUFFICIENT RADIAL DEPTH SO THAT A CRACK IS FORMED DUE TO COMBUSTIONPRESSURES BETWEEN THE INNER AND OUTER SURFACES OF THE SOLID PROPELLANTCHARGE ADJACENT THE NOTCH, AND SEALING MEANS IN THE NOTCH TO SEAL OFFTHE OUTER SURFACE OF THE SOLID PROPELLANT CHARGE FROM THE BURN AREA,SAID CRACK PROVIDING INCREASED BURN AREA.